The invention relates to an internal combustion engine arrangement having an exhaust gas recirculation (EGR) circuit.
As it is well know, an internal combustion engine may comprise a series of cylinders, an intake circuit for circulating intake gases to the cylinders and an exhaust circuit for collecting and evacuating exhaust gases from said cylinders. Many modern engines are now equipped with a turbo-charging system to enhance their efficiency, thereby having at least one turbine located in the exhaust circuit for recovering energy from the exhaust gases. For reasons mainly related to a better control of noxious emissions by the engine, it is well known to equip the engine with an EGR circuit connecting the exhaust circuit to the intake circuit to incorporate a portion of exhaust gases in the intake gases.
The portion of the exhaust gases which circulate in the EGR circuit, which will be referred to hereinafter as EGR gases, are those gases which result from the combustion of the air/fuel mixture in the cylinders. EGR gases comprise mainly carbon dioxide and water, but may also comprise nitrogen oxides, un-burnt hydrocarbons, carbon monoxide and other residues such as particles and soot. Among all these components, water is certainly the least harmful component in terms of pollution, but it nevertheless raises some difficulties. Indeed, it has appeared that at least in some EGR circuit designs, the water contained in the EGR gases, initially under vapor form due to the temperature of the exhaust gases, may condense in the EGR circuit. Of course, the risk is maximum in engine arrangements where the EGR circuit comprises a cooler to cool down the EGR gases before they are introduced in the intake circuit, and it is of particular relevance when the engine has not reached its full operating temperature, while starting and/or under cold temperatures.
The amount of water which may condense will vary according to the engine design, but also depending on the type of fuel burnt in the engine. Although water condensation may happen in petrol engines, in Diesel engines and in gas engines, it has proved to be particularly important in the case of gas engines, simply because the amount of water produced by the combustion of gas is proportionally more important than with other fuels.
Water condensation in the EGR circuit may lead to undesired results. First, the water will tend to accumulate at any low position point in the EGR circuit, that is any point of the circuit which has an altitude lower than its neighboring points on both sides. It is to be noted that a given circuit may comprise several low position points. Such low position points may be in a conduit portion of the circuit, in a cooler assembly or can be located at a valve level when the valve is closed. The amount of water which may condense can be quite important, especially during engine start-up.
If the accumulated water is still present when the engine is shut down, it will stay at least until next start-up, and may cause corrosion issues at the low position point. Another potential problem is that, at certain times, a quantity of accumulated water may burst into the intake circuit and be fed, still under liquid form, to the cylinders. If the amount of water thus fed to the cylinders is not insubstantial, it may severely affect the combustion process, resulting in engine jerk and increased production of noxious compounds in the cylinder.
In order to prevent such problems, it has already been suggested to equip the EGR circuit with drain systems to prevent or at least remove accumulated water.
Document JP-2001.193578 discloses an EGR circuit having a drain valve. The drain valve is a normally-open ball valve where the ball is spring-biased to the open position in the absence of pressure in the EGR circuit, so as to permit condensed water to escape. As soon as the EGR circuit is under pressure, the ball valve is automatically closed. Such a pressure controlled valve does not allow accumulated water to be drained when the EGR circuit is in use. The drain valve is arranged at a low position point in the EGR circuit, very close the exhaust circuit, and when the valve is opened, it discharges directly in the atmosphere, which is of course not optimum due to the fact that noxious substances may be discharged to the atmosphere, amounting to pollution
Documents JP-7.269417 and JP-8.46964 both disclose an EGR circuit with a condensed-water collector which can be drained through a dedicated controlled purge valve. The valve discharges directly to the atmosphere, with the above mentioned pollution problem, and this dedicated controlled valve represents an increased cost.
Document JP-2005.256.679 shows an engine having an engine arrangement where a dedicated controlled drain valve is provided at a low position point in the intake circuit between the EGR mixer and the intake manifold.
Document JP-2006-274961 shows an EGR circuit with a dedicated drain conduit which connects the EGR circuit to the exhaust circuit and which is equipped with a cyclone-type gas/water separator having a dedicated controlled drain valve. The separator is of course a cumbersome apparatus, also representing an additional cost in addition to the cost of the dedicated controlled valve.
Document US-2007/0084206 also shows an EGR circuit with a dedicated drain conduit which connects the EGR circuit to the exhaust circuit and which has a dedicated controlled drain valve, with one embodiment having the drain valve combined with the conventional EGR valve as a three way valve. As in the previous document, the drain valve is connected to the exhaust circuit downstream of the turbine of a turbo-compressor. In the latter document, the drain valve appears to be only opened when the EGR valve is closed, so that no draining appears to be possible when the EGR is required.
In view of the above, it appears the there is still the need for a cheap solution to the problem of water accumulation which nevertheless does not cause unnecessary pollution of the ambient air and may nevertheless operate in a wide range of engine operating conditions.
An aspect of the invention provides for an internal combustion engine comprising:                an EGR circuit (32) connecting a exhaust circuit (20) to an intake circuit (16) to incorporate a portion of exhaust gases in the intake gases,        at least one turbine (26) located; and        a dedicated drain conduit (46) which connects the EGR circuit (32) to the exhaust circuit (20);characterized in that the EGR circuit comprises at least one low position point and in that the dedicated drain conduit permanently connects said low position point of the EGR circuit to the exhaust circuit upstream of said turbine.        
According to other features of an engine arrangement:                the engine may comprise one or several cylinders;        the intake circuit is designed for circulating intake gases to the cylinder(s);        the exhaust circuit is designed for collecting and evacuating exhaust gases from said cylinder(s):        the turbine located in the exhaust circuit is designed for recovering energy from the exhaust gases.        